Trench Semiconductor Layout With Current Spreading Region for Lower Rdson
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Solution Overview
Problem
Power semiconductor devices face a trade-off between area-specific on-resistance (Rdson) and gate-to-drain charge (Qgd), with the depth of the gate trench and oxide thickness at the bottom of the gate trench being critical factors that require careful adjustment to optimize performance, but varying these parameters does not significantly improve the trade-off between Rdson and Qgd.
Innovation Solution
Incorporating a current spreading region at the bottom of the gate trenches with a higher average doping concentration than the drift zone, which reduces on-state resistance (Rdson) and improves the trade-off between Rdson and Qgd, allowing for better optimization by adjusting the dopant concentration rather than geometric properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gate trench is structured deeper into the drift region, then the spreading resistance is reduced, but Qgd is higher
Solution Approach 1:
The patent applies local quality by creating a current spreading region with higher doping concentration specifically at the bottom of the gate trench, while keeping other regions with their original doping levels. This localized doping enhancement reduces spreading resistance without requiring a deeper gate trench structure, thereby avoiding the penalty of increased Qgd.
Solution Approach 2:
The patent changes the doping concentration parameter locally at the bottom of the gate trench to create a current spreading region. This parameter change enables better current distribution and reduced spreading resistance without modifying the gate trench depth, thus resolving the trade-off between spreading resistance and Qgd.
2Reliability
If the gate trench depth is increased to optimize Rdson, then Rdson is reduced, but Qgd increases
Solution Approach 1:
Instead of uniformly increasing gate trench depth throughout the device, the patent applies local quality by selectively increasing the doping concentration only at the bottom of the gate trench. This localized modification optimizes Rdson through improved current spreading without the need for increased trench depth, thereby avoiding increased Qgd.
Solution Approach 2:
The patent optimizes Rdson by changing the doping concentration parameter at the bottom of the gate trench rather than changing the geometric parameter (trench depth). This parameter substitution allows Rdson optimization while maintaining the original trench depth and avoiding Qgd increase.
3Reliability
If the oxide thickness at the bottom of the gate trench is varied, then device optimization is attempted, but the optimization effect is limited compared to gate trench depth variation
Solution Approach 1:
The patent changes the doping concentration parameter at the bottom of the gate trench, which proves to be a more effective optimization lever than oxide thickness or gate trench depth. This parameter change provides significant device performance improvement with controlled complexity, as doping can be precisely controlled through standard semiconductor fabrication processes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The current spreading region reduces Rdson by up to 13% and improves the trade-off between Rdson and Qgd, making it easier to optimize the device performance compared to varying the gate trench geometry, while maintaining acceptable breakdown voltage.
Implementation Method 1
a current spreading region of the first conductivity type at the bottom of the gate trenches and having a higher average doping concentration than the drift zone
Data Source
AI summary
A semiconductor device includes: a semiconductor substrate; a drift zone of a first conductivity type in the semiconductor substrate; an array of interconnected gate trenches extending from a first surface of the semiconductor substrate into the drift zone; a plurality of semiconductor mesas delimited by the array of interconnected gate trenches; a plurality of needle-shaped field plate trenches extending from the first surface into the plurality of semiconductor mesas; in the plurality of semiconductor mesas, a source region of the first conductivity type and a body region of a second conductivity type separating the source region from the drift zone; and a current spreading region of the first conductivity type at the bottom of the gate trenches and having a higher average doping concentration than the drift zone. Methods of producing the semiconductor device are also described.